I live in Central West FL and I must admit, I avoid WDW then. It is hot so expect it. Depending on where you are coming from, it can be quite uncomfortable.
I am originally from the NE and they had a much hotter summer last year than FL did so if you are use to hot, humid summers, it pretty much is just that here in CF.
My best advise is go early, leave mid day and go back in the evening. It's the best way to survive. If I do go in the heat, I try to revolve the things I do so they include an indoor thing.
Do a couple of rides and then go sit inside some where or go into a shop or two for a good 15 min to cool down.
Drink more than you think you should. FL heat sneaks up on you and you can be in trouble fast. If you normally drink one bottle of water every 2 hours or so, drink 2 or three in FL. Yes it's more potty breaks but worth it.